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Thursday, December 06, 2012
Fight fire with fire
21:06
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FIGHT
FIRE WITH FIRE
Fight fire with fire, not chemical warfare.
Controlling pest insects these days using chemical sprays have caused a great
amount of concern to both gardeners and consumers in general. Concerns that
involve our environment, the health of our children, pets and for the gardeners
themselves who are dispensing such chemicals or are working with the plants
after they have been sprayed. Unfortunately, many of these chemicals are
"non-selective" in other words, they don't just kill the target pest,
they tend to kill an entire range of insects, both good and bad.
Today's biggest concern is where toxic products
are applied to products that are grown for human consumption. As a result, many
indoor gardeners have turned to using beneficial insects to control their pest
problems.
Just
what are "beneficial" insects? Beneficials are insects that help
gardeners by killing pest insects and eliminate the need for using toxic
chemicals. Mother Nature has developed her own system to balance out or
regulate pest infestations, by using the "good bugs" to control the
"bad bugs".
Beneficial insects eliminate pest insects
generally in one of two ways. They either parasitize them or hey are a
predator of them.
Parasitic beneficial insects actually depend on
pest insects for their survival because they must lay their eggs in or on them.
The immature stages of the beneficial insect actually develop in or on the "host" pest insect, feeding
on its body and thereby killing the "host".
Predator beneficial insects are beneficial
insects that actually eat the pest insect. Therefore, they actually depend on
the pest insects for their survival.
Some of the most effective beneficial insects are
a group known as parasitic wasps. These wasps usually lay their eggs inside a
specific pest, while the pest is very young - in the egg, larval or pupal stage
of their life. These wasps are incredibly tiny, generally not even one-tenth
the size of the wasps that will sting you and are almost impossible to see with
the naked eye - the largest parasitic wasps are generally no bigger than a 1/4
of an inch and the smallest being the size of the period at the end of this
sentence. The "host insect" generally are not as lucky as we are, for
the wasps' larvae develops inside the pest, the pests die and then the wasps
thrive and emerge looking for a new host in which to lay their eggs and
continue on the cycle.
Most wasps seek out only one species of pest, for
instance Encarsia Formosa, seeks out only the whitefly eggs. Encarsia lays eggs
inside the whitefly eggs (this is when the whitefly is at an immobile stage). When
the Encarsia eggs hatch, the larva feeds on the whitefly embryo, then forming a
pupae inside the whitefly egg, killing it if they hadn't already. The adult
Encarsia wasp emerges from the whitefly egg casing by chewing an exit hole and
flies off in search of a new host to lay its eggs. A female Encarsia can lay
between 50 to 100 eggs in a lifetime - which is excellent when you consider
that their "lifetime" is only two to three weeks.
In order to keep these beneficial insects in your
greenhouse you need to supply them with the essentials for life; food and
water. Generally most parasitic wasps like nectar, the sugary fluid secreted by
flowers. If the wasps have the essentials for their survival, they will live
longer and thus seek out more host insects to lay their eggs, thus eliminating
more pest insects, as well creating successive generations of biological
control.
Remember that the smaller the wasp, the greater
the need for plants with small flowers, where the nectar is easier for the wasp
to get at. A great plant to grow for beneficial wasps is dill. Even though the
plant grows tall, it has hundreds of tiny flowers clustered together which make
the nectar in these tiny flowers easy for tiny wasps to flock to. Other good
plants to grow to help keep beneficial wasps around are fennel, caraway,
parsley and coriander. I took a close look at my parsley plant just the other
day. The flowers were emerging on some of the stems and it had three ladybugs
crawling on it, feeding on the nectar - and hopefully other pests that had also
took up residence. In a period of five minutes while I was sipping on a cup of
tea, the parsley also had three bumble bees visit it. Keep in mind my parsley
plant is out of doors, however I will be planting one in my newly constructed greenhouse!
Parasitic wasps visit the tiny flowers for
nectar, but the predator insects also stop by to eat the pollen, especially
juvenile and adult ladybugs and lacewing.
Nematodes migrate through growing medium finding
insect larvae by detecting either a slight increase in temperature or release
of methane gas. Once they have found a "Host", the nematode enters
the host body through natural openings such as the mouth. Once inside the host,
they release a symbiotic bacteria that paralyzes the host and kills it within
24 - 48 hours. The nematodes feed on the bacteria and the decomposed host
tissue where they reproduce until their numbers drive them out to find a new host.
Larvae nematodes can survive without a host for up to a year provided moisture
levels and temperatures remain favorable for them.Nematodes
require a moist, dark environment. Provided soil temperatures are kept
consistent for indoor growing, you will not have to worry about the nematodes
hibernating. It is only when there is a drop in temperature during the the
winter that nematodes will burrow deeper in the soil and begin hibernation; as
temperatures rise in the spring they move closer to the soil surface.
Unfortunately, their return usually lags behind that of soil pests. So for the
most effective control re-introduce beneficial nematodes early each spring or
each time the growing medium is changed.
Beneficial Nematodes will control over 250
different species of soil pests including some of the most damaging, like
weevils, wire worms (particularly damaging to new plants), fungas gnats, grubs,
earwigs, sow bugs and pill bugs. The majority of soil pests can be controlled
with regular applications of beneficial nematodes, in the spring and fall or
each time the growing medium is changed.
Predators also include Mites. Two-spotted Spider
Mite is generally a huge problem for indoor growers. They have a lifecycle of
15 days, but can reap an incredible amount of damage in that time - as well the
female can lay a further 50 - 100 eggs. All stages of spider mite development
cause plant damage, by the spider mite feeding on plant cells. The cells will
turn yellow which cause a speckling of the leaf. When the damage is increased
the leaf will turn completely yellow and die off. If you believe you have
spider mites, you can generally find them by looking on the underside of your
plants leaves. When you start to see webbing on the plant, it means that your
spider mites have reached infestation levels.
But incredibly, one of the best controls for
spider mites is a predatory mite - Phytoseiulus Persimilis. Persimilis is a red
pear-shaped mite with long legs. Be careful not to confuse summer spider mites
that turn orange or deep when they hibernate with Persimilis.
An adult Persimilis will eat 5-20 prey (eggs or
mites) per day. What makes them so effective against spider mites is that they
reproduce more quickly at temperatures above 28°C (82°F) than the spider mite
and they feed on all stages of the pest spider mite. However, Persimilis must
have high humidity temperatures - above 60% , which also affect the pest spider
mite to reduce their egg laying.
Persimilis are very voracious and have one of the
highest consumption rates. Almost 75% of European greenhouse vegetable
production relies on Persimilis for spider mite control, and the California
strawberry industry also use this species for control. Persimilis is also used
in interior plantscapes and conservatories and greenhouse ornamentals growers
have long relied on their ability to control pest spider mites.
Because these mites are such efficient hunters
and dispersers, they can cause extinction of their spider mite prey, which is
extremely desirable where little or no spider mite damage can be tolerated,
such as in ornamental plants. Typically, Persimilis will eventually exhaust
their food supply and starve and so it must be reintroduced when new spider
mite infestations occur.
Another excellent predator for spider mite is the
predatory midge, Feltiella Acarisuga. This midge is about 1/12 of an inch long
and is a pinkish brown colour. The female Feltiella will lay its eggs inside
the spider mite colony and as soon as the young larvae hatch, they begin their
feast on spider mite eggs. The young larvae feed mainly on the eggs while the
older larvae feed on all stages of spider mite. A larval Feltiella can feed on
about 50 spider mites before pupating. The lifespan of the Feltiella from egg
to adult is 10-15 days and the female will lay about 12-14 eggs. Like
Persimilis, when the food supply is exhausted they will also starve and thus
must be reintroduced when new infestations occur.
Some of the best beneficial predators to purchase
are the ones that will stay around after you release them - especially the ones
that haven't developed their wings yet.
Voracious aphid eaters are lacewing larvae and
ladybug larvae, these are such good eaters because in essence they are
teenagers with huge appetites and are not yet sexually active and distracted
from the task of eating! These larvae generally stay and "clean-up"
much better as they are only able to crawl in search of their meal, and they
haven't developed their wings to fly away in search of a mate. The adult
ladybug will eat the aphids, however as lacewing become adults they become
strictly pollen feeders.
For gardeners the best control recommendation is
to use a combination of controls i.e. parasite and predator for control of a
problem. An excellent example is aphid control: use adult ladybugs to eat the
adult aphids, as well to lay eggs in the colony of aphid eggs, but also use
Aphidius Colemani (a parasitic wasp) to control the eggs and larvae.
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